1. Field of the Invention
The present invention relates, in general, to magnetic data storage, and, more particularly, to a read/write head and method for operating a read/write head to improve perpendicular recording performance.
2. Relevant Background
Magnetic recording is a predominant method for mass data storage, and is expected to remain a predominant method for the foreseeable future. Demand for hard disk drive capacity, for example, is doubling every year. There is continuous pressure to decrease the cost per byte of mass storage devices. As a result, magnetic storage device manufacturers strive to provide higher capacity and faster performance from hard disk drives.
At one time, capacity could be increased simply by providing more disks and more read/write heads in a single enclosure. However, space and power requirements make the prior practice of simply adding more disks and heads to a hard drive less and less effective. Hence, disk drive suppliers continue to increase areal densities, or the number of data bits per square inch of recording media, to meet the increasing demand for storage at competitive pricing. Read and write head design are key technologies needed to achieve these capacity increases.
Magnetoresistive (MR) head technology is used to provide high areal density. MR head structures include an MR element as a magnetic field sensor. A coil is formed above the read head and surrounded by a magnetic yoke that defines a write gap. The write gap is positioned over the MR element in an integrated structure. MR head technology uses separate read and write devices that allow each device to be optimized for one particular function (i.e., reading or writing data). Magnetoresistive devices or heads utilizing giant magnetoresistance (GMR) are of current technological interest to achieve high areal density recording. Magnetic field sensors based on the GMR effect are designed to measure or sense magnetic field strength. GMR sensors have greater output than conventional anisotropic magnetoresistive (AMR) sensors. GMR sensors directly detect the magnetic field rather than the rate of change in magnetic field (i.e., flux) therefore, they are useful as read heads for sensing data stored on magnetic media. The output of GMR sensors is frequency insensitive and the sensor produces an output even in a constant magnetic field. GMR devices are sensitive to small magnetic fields and because they are physically small, they promise higher areal density for magnetic storage devices. These factors make a GMR sensor a desirable choice for read heads.
Most conventional magnetic recording mechanisms use a longitudinal recording technique in which the magnetic field produced on the recording media is stored in the media surface and is oriented longitudinally. Longitudinal recording systems result in magnetic fields that are localized to the surface of the recording media and have been favored because media with longitudinally oriented magnetic particles have been easier to produce.
More recently, manufacturers are considering perpendicular recording systems in which the magnetic field produced in the media is oriented perpendicular to the media surface. Perpendicular recording promises data recording at much higher areal densities as the magnetic field is stored vertically within the media rather than simply on the media surface. Essentially, because the magnetic field indicating a bit of data is stored using the entire volume of the media rather than just the surface, significantly higher areal densities can be achieved.
However, perpendicular recording systems use a magnetically soft underlayer that require requires relatively low fields to become magnetized. As a result, perpendicular recording systems have been more sensitive to stray fields by a factor of 3 to 10 as compared with longitudinal recording. Perpendicular error rates are strongly affected for applied fields of about 10–15 Oersteds (Oe), as compared with 30–50 Oe for longitudinal recording.
Stray field sensitivity degrades performance in environments where ambient magnetic fields exist, such as in the vicinity of motors, electric currents, and magnets. For example, when disk drives are mounted in an enclosure in close proximity, the drive motors produce sufficient fields to interfere with adjacent disk drives. Fields outside of a drive can be in the range of 100-105 Oe, which can affect nearby drives. Similarly, nearby tape drives can produce significant stray magnetic fields. The increasing use of disk drives in devices such as televisions, automobiles, and portable computers promises increased demand for drives that have low stray field sensitivity.
It has been noted by the inventors of the present invention that the structures used in conventional read/write head devices, particularly in read/write devices for perpendicular recording, capture the stray magnetic fields and couple the stray magnetic fields to the recording media in an undesirable fashion. These structures include shields around the read head that are intended to block fields produced by neighboring portions of the recording media so that the read head reacts only to magnetic fields produced in an area directly under the read device. Similarly, the pole or poles in the write head are engineered to promote perpendicular fields, and consequently are sensitive to capturing stray perpendicular fields. Accordingly, a need exists for a recording system and a method for operating a recording system that reduce sensitivity to stray fields, especially in perpendicular recording systems.